The subject invention is directed to the pressure sensor arts and, more particularly, to pressure sensor apparatus suited for use in automotive applications to sense the pressure of a pressurized fluid medium and generate electrical signals representative of the sensed pressure.
Pressure sensors of the type under consideration are well known in the automotive engineering community. A multiplicity of designs have been used in automotive applications such as, for example, as sensor elements for monitoring the oil pressure of an engine or to monitor brake pressure, or the like.
Generally, pressure sensor units typically comprise a housing having an inlet opening adapted to receive a small quantity of the pressurized fluid medium intended to be monitored. Typically, the pressurized fluid medium is conducted into the housing via the inlet opening towards a pressure measuring cell located within the housing. Many pressure sensor housings are provided with external threading so that the housing can be screwed into place on an engine block or brake cylinder having corresponding intermateable threads.
On important consideration in pressure sensors used for automotive applications is their long-term stability and resistance to aggressive media as well as survivability in rough environmental conditions. One proposed solution to protect the pressure sensors from aggressive fluids that may cause damage has been to provide a barrier between the pressure sensor and the fluid. Sensors of this type are known in the art as "media-separated" pressure sensor units. There, the monitored pressurized fluid medium does not come into actual direct contact with the sensor element itself but, rather, acts indirectly upon the pressure sensing device through an intermediary separation membrane. In these designs, the sensitive sensor element disposed within the housing is typically arranged in a measuring cell housing which is in turn protected from aggressive fluid medium by means of the above-noted separation membrane. An interstitial pressure transfer medium is often used to transfer the pressure generated by the fluid medium to be monitored to the sensor element. Normally, the pressure transfer medium occupies the void between the separation membrane and the sensor element proper. Pressure sensor units of this type are well known in the art and are described in the literature including German Patent DE 295 11 996 U1.
One disadvantage of media-separated pressure sensor units, however, is that it is often difficult and costly to install the pressure measuring cell into the housing. Typically, the pressure measuring cell comprises one or more housing components and a fragile sensor element arranged therein. Major contributors to the difficulty and expense in fabricating the media-separated pressure sensor units include the step of installing the pressure sensor element on one or more appropriate support elements and further, the step of establishing electrical and mechanical connections to the sensor element.
Inasmuch as all sensor elements must be positioned in a manner to enable the measured fluid to act upon the sensor element, it is necessary to route the electrical pressure sensor connectors on a side of the support element facing away from the pressurized fluid medium. Typically, the electrical connections are not routed toward the pressurized medium. Normally also, in order to absorb and transfer the high pressure forces generated by the pressurized fluid medium to the housing, the support elements are usually formed of metal. Accordingly, routing the electrical connections on a side of the support element facing away from the pressurized fluid medium is difficult. It is well known that metal support elements conduct electricity. Therefore, in pressure sensors that use metal support elements, it is necessary to extend the sensor electrical connection contacts in an isolated fashion through the metal support element on a side opposite the pressurized fluid medium. An example is shown in DE 295 11 976 U1. The complexity of the electrical connections in pressure sensors of this type is commensurate with the expense thereof.
A alternative pressure sensor is described in German patent application DE 196 37 763 wherein a pressure sensor unit includes a measuring cell having a measuring cell housing retained in the main housing of the pressure sensor unit. In that example, the measuring cell housing is provided with a central breakout portion whereat a pressure sensor element is installed from a rear side of the breakout portion. The pressure sensor element is located in a TO-type housing. The TO-type housing is tightly joined with the measuring cell by means of welding. It is an advantage of the above-described construction that the sensor element proper can be pre-installed in the measuring cell housing and joined thereto before the pressure sensor unit itself is constructed. In contrast to prior known sensor units, this results in the benefit of a less complicated installation. One expense that remains, however, is a result of the need to install the sensor element proper into the TO-type housing. Further, an additional expense drawback is the requirement for the firm and tight joining of the TO-type housing to the measuring cell housing.
It is desirable, therefore, to provide a pressure sensor that is able to withstand aggressive fluid media and rough environmental conditions while being simple and relatively inexpensive to construct.